Regarding the issues you note I am no more scared for Chicago than I am for the rest of the world.
I am concerned about the yuppification of much of the city, though that is one blessing of the bursting housing market bubble. The incentive for greedy developers to throw up housing solely for a buck is gone because the values have dropped too much to make it worthwhile. We need to have housing for all income levels - rich people need poor for services and they can't all drive in from Gary.
You know how crowded Lake Shore Drive is - now throw on the tallest residential structure in the world. Traffic in Streeterville is bad enough -can you imagine how awful it will be when/if the Spire goes up?
Willis Tower / Sears Tower is sad but hardly a cause for concern. One bright side is that Willis is moving in to create jobs. They could had moved to Milwaukee, Indianapolis, or a cheaper-rent suburb...like Sears did!
Jerry Springer is moving but Oprah is still here. That means the IQ of the city just went up about five points.
No this will not become another Detroit. K-Mart bought Sears, then moved out of the Detroit area (Troy, MI specifically). Chicago is not dependent on one industry like Detroit is, not even close.
Yeah that would really suck if that overgrown suburb called Houston overtakes us. Los Angeles already did that in the 70's - is LA a better city? I think not. What Houston may gain in quantity we will always surpass with quality. Minute Maid Stadium or Wrigley Field? NOOOO contest!